According to a recent study published on Analytical Chemistry, a novel focusing quadrupole ion funnel (FQ-IF) was proposed by researchers from the Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS).
The funnel took advantage of radio frequency ion focusing technology in Proton transfer reaction mass spectrometry (PTR-MS), which greatly improved its sensitivity and endowed it with better "sense of smell."
PTR-MS is an important analysis technique for the real-time detection of volatile organic compounds (VOCs). Detection sensitivity is a critical performance in PTR-MS. The successful determination of trace VOCs lies on the sensitivity of the instrument, so sensitivity enhancement is a pursued topic in PTR-MS.
"The FQ-IF drift tube we developed in this study could improve ion transmission efficiency," said BAO Xun, first author of the paper, "and have a suitable collision condition."
He further explained its structure. The tube consisted of 20 layers of stainless steel electrodes, and each layer had 4 quarter rings. The first 6 layers had a constant inner hole diameter of 22 mm. The latter 14 layers tapered the inner diameter down to 8 mm. The ion transmission efficiency in the drift tube was improved by the radio frequency electric field, which was key to sensitivity-improvement and offered more possibility for PTR-MS.
The sensitivity of the FQ-IF range now was 13.8 to 87.9 times higher compared to the conventional direct current drift tube, and 1.7 to 4.8 times higher compared to the ion funnel drift tube.
The improvements in the limit of detection (LOD) for the FQ-IF ranged from 2.7 to 35.7 times compared to the conventional direct current drift tube.
In addition, the FQ-IF drift tube could easily be coupled to other types of mass spectrometers to increase the detection sensitivity and may offer considerable benefits.
This work was supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of CAS, the Anhui Provincial Key R&D Program, and the HFIPS Director's Fund, etc.
The focusing effect of the FQ-IF drift tube. (Image by BAO Xun)